With the proliferation of electrically operated portable ‘gadgets,” the number of batteries sold to power these gadgets has mushroomed proportionately. One type of battery whose sales have increased dramatically over the past 10 years is lithium batteries. For example, it is estimated that about 4 million dollars of lithium batteries were sold in 1996, and that about 4 billion dollars in lithium batteries were sold in 2014.
Lithium batteries have advantages over the alkaline batteries that they usually replace. Because since lithium is a very active material, it tends to provide greater power relative to the amount of material used in a battery. Additionally, the lithium discharge curve is longer and flatter than alkaline, thus providing consistent higher voltage to the life of the battery.
These characteristics enable a gadget manufacturer to reduce the size of batteries of equivalent power required to operate the gadget, or alternately to provide a greater amount of power in a battery in a determined size.
Although lithium batteries are more expensive than alkaline, they have especially good performance characteristics when used in small devices or those requiring a large amount of reserve power, such as cameras and smartphones.
The term “lithium battery” refers to a class of batteries that include cathodes or electrolytes that contain either metallic lithium or a lithium compound. The two primary categories of lithium batteries include lithium metal batteries and lithium-ion batteries.
There are several important differences between the lithium batteries and the lithium ion batteries. The most important practical difference between the two is that lithium batteries are not rechargable, whereas lithium ion batteries are rechargable. From a chemical standpoint, lithium batteries use lithium in its pure metallic form, whereas lithium ion batteries use lithium compounds that are much more stable than the elemental lithium used in lithium batteries. Although lithium batteries should never be recharged, lithium ion batteries are designed to be recharged hundreds of times.
Another advantage of lithium batteries as compared to other rechargeable such as nickel metal hydride rechargeable batteries or nickel cadmium batteries is that lithium batteries have a higher energy density than most types of other rechargeables. As such, for their size and weight, lithium ion batteries can store more energy than nickel based rechargeable batteries.
Additionally, lithium ion batteries operate at higher voltages than other rechargeable batteries, which enables single cell batteries to be used in many applications whereas a nickel metal hydride or nickel cadmium batteries would require multiple cells. Further lithium batteries have a lower self discharge rate than other types of rechargeable batteries, and therefor retain their charge for a longer period of time. In summary, lithium ion batteries can be made to be smaller, lighter, have a high voltage and hold a charge much longer than other types of rechargeable batteries.
Unfortunately, lithium batteries also have certain disadvantages when compared to other batteries. For example, lithium batteries can be more expensive to manufacture than alkaline and nickel based batteries. Another disadvantage of the use of lithium batteries is that they have a greater potential to catch fire than nickel based batteries.
It is believed that the root cause of the propensity of lithium ion batteries to catch fire is a failure or flaw in the separators within the batteries. Lithium batteries contain extremely thin separators that keep the elements in the battery apart. When these separators fail to function properly, the battery can fail and catch fire. These “bad separator” failures can result from poor design, manufacturing flaws, external damage induced on the battery, poor battery pack design, insufficient or inadequate protection being engineered into the design of the battery, and over charging.
The internal short circuit that results from damage to the thin separator results in the subsequent build up of heat. This build up of heat in a particular battery can trigger what is known as a thermal runaway in which the battery will overheat and bursts into flames, and thereby ignites adjacent batteries in much the same manner that a lit match within a pack of matches will ignite adjacent matches if the lit match gets close to the adjacent unlit matches.
In this regard, it has been recorded that lithium-ion batteries ignite at about 953 degrees F., and can reach temperatures that exceed 1100 degrees F. while burning. As such, a burning lithium ion battery can generally generate enough heat to cause adjacent batteries to also ignite.
This ability of batteries to ignite other batteries is referred to as a “thermal runaway”. One factor that exacerbates thermal runaway is that lithium batteries are capable of burning and igniting without the presence of oxygen. As such, placing the batteries in an evacuated container, or a sealed container will not prevent the batteries within the container from engaging in a thermal runaway and thereby overheating the container.
Instances have been reported where a multi-battery container engaged in thermal runaway caused an adjacent multi-battery containing containers to get hot enough so as to ignite the lithium batteries contained within.
This propensity to catch fire can increase the risk to shippers who transport lithium batteries, especially when the batteries are shipped on board an aircraft. The increased risks of transporting the batteries increases the cost of transporting the batteries.
Transportation costs can contribute significantly to the cost of the batteries, especially in view of the fact that most batteries are sold today are manufactured in China, but may be used in distant markets, such as the North American and European markets.
A thermal runaway can create an especially problematic situation in an airplane that is carrying a load of batteries. Testing conducted by the FAA Wiliman J. Hughes Technical Center (“FAA Tech Center”) indicates that there are particular propagation characteristics that are associated with the lithium batteries. The chain reaction thermal runaway can lead to self-heating and release of a battery's stored energy. In a fire situation, air temperature in a cargo compartment fire may rise above the auto ignition temperature of lithium. As discussed above these high temperatures can ignite and propagates ignition of adjacent batteries, and thereby create a risk of a catastrophic fire event in the cargo compartment.
Although improvements in lithium ion battery construction have made such thermal runaway extremely rare, the risk of a thermal runaway still exists.
Various attempts have been made to control thermal runaway. Most of these attempts have centered around the use of fire retardants or liquid suppression products technologies.
The underlying theory behind these attempts is to extinguish fire, and thereby reduce the effective number of burning batteries before the fires spread to adjacent batteries and/or adjacent containers and batteries, instead of preventing the first or thermal runaways from occurring. Unfortunately, these prior attempts have not been wholly successful in preventing thermal runaway with lithium batteries.
It will be appreciated that it would be useful to have a container that could limit the impact of such fires and explosions by providing a thermal barrier that reduces the heat transfer between adjacent containers, and thereby reduces the amount and size of the thermal runaway, and thereby reduce the heat and pressure generated in an area by the thermal runaway.
Superabsorbent polymers (SAPs) or hydrogels are loosely cross-linked, three-dimensional networks of flexible polymer chains that carry dissociated, ionic functional groups. They are basically the materials that can absorb fluids of greater than 15 times their own dried weight, either under load or without load, such as water, electrolyte solution, synthetic urine, brines, biological fluids such as urine sweat, and blood. They are polymers which are characterized by hydrophilicity containing carboxylic acid, carboxamide, hydroxyl, amine, imide groups and so on, insoluble in water, and are cross-linked polyelectrolytes. Because of their ionic nature and interconnected structure, they absorb large quantities of water and other aqueous solutions without dissolving by solvation of water molecules via hydrogen bonds, increasing the entropy of the network to make the SAPs swell tremendously.
The factors that supply absorbing power to polymers are osmotic pressure, based on movable counter-ions, and affinity between the polymer electrolyte and water. The factor that suppresses absorbing power, in contrast, is found in the elasticity of the gel resulting from its network structure. Not only are they of high fluid absorbing capacity, but the absorbed fluid is hard to release, as they merely immobilize the fluid by entrapment rather than by holding it in the structure. Process for their preparation are described, for example, in S. Kiatkamjornwong, “Superabsorbent Polymers and Superabsorbent Polymer Compositions, ScienceAsia, 33 Supplement 1 (2007): 39-43 and M. J. Zohuriaan-Mehr and K. Kabiri, “Superabsorbent Polymer Materials: A Review,” Iranian Polymer Journal, 17(6), (2008), 451-477.
There are a number of US patents that address the use of particulate superabsorbent dry polymers for use in fire prevention and fire extinguishing, including: von Blucher U.S. Pat. No. 4,978,460; von Blucher U.S. Pat. No. 5,190,110; and Pascente U.S. Pat. No. 5,849,210.